1. Field of the Invention
The present invention relates to an acoustic diaphragm molding die and an acoustic diaphragm producing method. In particular, the present invention relates to an acoustic diaphragm molding die and an acoustic diaphragm producing method using a cooling medium for cooling.
2. Description of the Prior Art
Conventionally, paper has been used as a material for an acoustic diaphragm. However, in order to improve characteristics as a diaphragm material and offer a wider selection of design including colors, an acoustic diaphragm made from a synthetic resin material by way of injection molding is now being spread.
Molding of these acoustic diaphragms is normally carried out by injection molding using a direct gate type metal mold, or a so-called cold gate. The cold gate is a technique for solidifying a synthetic resin portion remaining in a sprue gate and taking out it together with a molded product from an injection molding metal mold. By retaining the portion in the sprue gate in a solidified state, it is possible to move an acoustic diaphragm as a molded product to the next production step.
An injection molding consists of following steps: a step of measuring amount of a synthetic resin as a material, a step of injection of the resin material melted, a step of applying pressure, a step of cooling the injected resin material, a step of removal or eject from the metal mold, and a step of removal from the injection molding apparatus. The obtained product includes a portion solidified in a sprue gate, which portion is removed by way of press processing, so as to complete an acoustic diaphragm of, for example, cone shape.
By the way, thickness of an acoustic diaphragm is remarkably thin compared to ordinary synthetic resin products and accordingly, it is necessary to use as a material such a synthetic resin which will not be easily solidified. In other words, in order to be filled correctly in a cavity of a metal die, the synthetic resin material should have a high fluidity because the cavity is very narrow so as to be matched with the configuration of a diaphragm.
Consequently, the synthetic resin material filled in the cavity takes a long time to be solidified and a molding tact (one cycle time) tends to be prolonged, lowering the production efficiency, which in turn brings about increase of production costs.
One of the reasons which prolongs the molding tact is use of a cold gate. Most of the molding tact is used for cooling the synthetic resin remaining in the sprue gate.
It can also be considered to use, for example, a hot runner type so as to carry out molding without a cold gate. However, as has been described above, an acoustic diaphragm is very thin and the molding pressure is significantly increased. Practically, an existing injection molding apparatus cannot stand this pressure.